1. Field of the Invention
The present invention relates to a single-component developing apparatus which develops latent electrostatic images using a single-component developer in such various types of reproducing apparatuses as electrophotographic copying machines or laser printers.
2. Discussion of the Related Art
Various types of developing apparatuses which develop latent electrostatic images on a latent image receiving member and which produce corresponding visible images on recording sheets are well known. Many of these apparatuses use single-component developer in the developing process. A schematic illustration of a developing apparatus which uses a single-component developer comprised of magnetic toner is shown, for example, in FIG. 1.
The apparatus in FIG. 1 uses a single-component magnetic toner 10 and typically comprises a hopper 1 for storing magnetic toner 10 and a magnetic roll 22. The magnetic roll 22 is formed by attaching a plurality of magnetic poles to the inside of a cylindrical sleeve 21. The cylindrical sleeve 21 is disposed within a developing roll 2 so as to be freely rotatable. Thus constituted, the developing roll 2 magnetically attracts magnetic toner 10 to cylindrical sleeve 21. A developer regulating member 3 extends downward into hopper 1 restricting magnetic toner 10 into a developing area, and pressing magnetic toner 10 into a thin layer of predetermined thickness onto a peripheral surface of developing roll 2.
Thus, in the single-component developing apparatus described above, magnetic toner 10 stored in hopper 1 contacts cylindrical sleeve 21. As the developing roll 2 is rotated, a quantity of magnetic toner 10 in the range of from 0.5 to 2.0 mg/cm2 adheres to the peripheral surface of cylindrical sleeve 21 by the combined action of developing roll rotation and of the developer regulating member 3. The adhering magnetic toner 10 is transported to a developing area facing an electrostatic latent image receiving member 4. The transported magnetic toner 10 has a charge of predetermined value. A biasing DC power supply 6 and a high-voltage AC power supply 5 are connected to cylindrical sleeve 21. AC power supply 5 applies a DC biased AC sine wave voltage to the cylindrical sleeve 21. An electric field formed between electrostatic latent image receiving member 4 and developing roll 2 causes charged magnetic toner 10 to fly onto the electrostatic latent image receiving member 4 and form a toner image 8 corresponding to an electrostatic latent image 7.
In the single-component developing apparatus described above a so-called toner chain, that is magnetic toner 10 flying from developing roll 2 to electrostatic latent image receiving member 4 in a row configuration or "a chain" arranged along a line of the magnetic force applied to electrostatic latent image receiving member 4, is frequently generated because the magnetic force of magnet roll 22 fixed inside of developing roll 2 also affects the developing area. Unfortunately, therefore, in transferring toner image to recording sheets, the toner chain creates a "tailing" effect, that is, creation of a large number of fine particle lines at the end of the toner image such as shown in FIG. 13 (A). The toner chain may also scatter magnetic toner particles during the process and cause a "blur" effect shown in FIG. 13 (B). As a result, serious defects may occur in the transferred images.
Further explanation of the formation of the toner chain in cases where DC biased AC voltage is applied as a developing bias voltage follows. As mentioned above, magnetic toner 10 formed into a thin layer on the developing roll 2 flies onto the electrostatic latent image receiving member 4 as the result of an alternating electric field biased with a DC developing bias voltage component. However, magnetic toner 10 does not fly straight onto the electrostatic latent image receiving member. Rather, it wavers in a gap separating developing roll 2 and electrostatic latent image receiving member 4 as the direction of the alternating electric field changes until it adheres to the electrostatic latent image receiving member 4. In other words, upon application of the developing bias voltage, which has a sine waveform as shown by the dotted line in FIG. 3, magnetic toner 10 is either attracted towards the electrostatic latent image receiving member 4, or towards the developing roll 2. As a result, magnetic toner 10 largely wavers in the magnetic field near the center of the gap between developing roll 2 and electrostatic latent image receiving member 4 as shown in FIG. 4., and adheres to the electrostatic latent image receiving member 4 only by being attracted to the electric potential of the electrostatic latent image 7 as it comes into a peripheral portion of the gap where the electric field has a less effect. Accordingly, adhering magnetic toner 10 is influenced by the magnetic field (shown as broken lines in FIG. 4) more strongly than by the electric field, and the range of influence along a toner chain varies along the lines of magnetic force.